1. Field of the Invention
The present invention relates to mutual active noise and vibration cancellation and in particular to a multi-fan apparatus incorporating at least two fans which mutually cancel each other's noise and/or vibrations.
2. Description of the Related Art
Many electronic systems, such as computer systems, require active cooling in order to maintain component temperatures at acceptable levels. Active cooling is usually accomplished by air moving devices, such as blowers and fans, with rotating components (e.g., blades, rotors, and other rotating machinery). All such air cooling devices shall be referred to herein as fans. Modern computer systems generate so much heat that these fans must be very powerful, and therefore generate a large amount of noise and vibration. The amount of noise that can be produced by an electronic system is limited by safety and regulatory agencies in this and other countries. Fan noise may thus impede sales into countries and environments with stringent noise standards. Since noise production is directly related to a fan's air cooling capacity, these noise standards also effectively impose a constraint on the processing power that can be installed into a computer system.
Today several techniques are used to reduce fan noise and vibration. Fans are isolation-mounted, baffled, and sculpted to reduce conducted and radiated noise. Fan blades may be constructed out of soft materials that limit noise radiation. However, these techniques are reaching the limits of their effectiveness, and are already commonly in use. In some environments active noise cancellation is used, wherein speakers, microphones, and a feedback circuit launch an inverse sound wave that destructively interferes with the original unwanted noise. This technique is currently considered too costly for inclusion into modern computer systems.